Light emitting diode (LED) is a junction diode produced with a wafer that includes a semiconductor substrate, and p-type and n-type crystalline layers formed on the substrate. After the crystalline layers are formed on the substrate, the produced wafer is cut into chips having desired dimensions. The cut chips are fixed onto a panel, wired, and packaged to produce a plurality of LED bulbs. Generally, the LED is packaged with epoxy resin.
The LED has become indispensable to modern society and may be differently designed for a variety of applications. Since the LED is generally used in lighting, warning, and visually emphasized advertising devices, it is important to effectively reduce the volume thereof and enhance its power in creating even better visual effect.
FIG. 1 is a schematic sectional view of a conventional LED package. As shown, an LED element included in this type of conventional LED package has a first lead frame 11 and a second lead frame 12. The second lead frame 12 is formed at a top with a cup-shaped recess 13, to a bottom of which an LED chip 14 is positioned and electrically connected to the first lead frame 11 via a solder wire 15. A sealing material 16 is then applied to outside of the LED element to seal the same. Typically, the sealing material 16 is a transparent material, such as epoxy resin, to allow transmission of light emitted from the LED chip 14.
In an advertising means that uses LED elements and requires colorful light sources, a plurality of LED's providing different color light sources, usually red, green, and blue LED's, must be prepared and then soldered to a circuit board according to a predetermined pattern. A control box is provided to control the on/off and flashing of the LED's. In this case, a large quantity of LED's showing different color light sources must be prepared and soldered onto the circuit board one by one. The soldering is time-consuming and a large number of soldering points increase the chances of high bad yield due to poor soldering. Thus, an illuminating device using the above-described type of LED packages has not only large volume but also high manufacturing cost.
A multi-chip LED is developed in an attempt to improve the conventional mono-chip LED that is not suitable for use on a device requiring multiple color light sources. The multi-chip LED mainly includes one single light-emitting element that is internally provided with a plurality of LED chips for producing different color light sources, including red, green, and blue light sources. That is, only one LED is enough to produce white or color light under control.
FIGS. 2 to 4 shows some examples of packaging structures for the multi-chip LED.
FIG. 2 is a schematic sectional view of a first conventional multi-chip LED package that forms one single light-emitting element. The light-emitting element includes a circuit board 21, to a top of which a plurality of, typically three, LED chips producing different color light sources are connected. The three LED chips generally include a red LED chip 22, a green LED chip 23, and a blue LED chip 24. By differently combining the color light sources from the three LED chips 22, 23, and 24 under control, white or other color light may be produced. The multi-chip LED package of FIG. 2 does not include a control unit. Therefore, an external control box must be additionally provided.
FIG. 3 is a schematic plan view of a second conventional multi-chip LED package that also forms one single light-emitting element. The light-emitting element includes a circuit board 31, to a top of which red, green, and blue LED chips 32, 33, and 34 are connected. There is also a controlling integrated circuit (IC) 35 provided on the top of the circuit board 31 and electrically connected to the three LED chips 32, 33 and 34 for controlling the on/off of the three LED chips to produce changeful color light. In the LED package of FIG. 3, the chips 32, 33, 34 and the controlling IC 35 all are located on the top of the circuit board 31 to result in a large volume of the circuit board 31.
FIG. 4 is a schematic sectional view of a third conventional multi-chip LED package that also forms one single light-emitting element. The light-emitting element includes a circuit board 41, to a top of which red, green, and blue LED chips 42, 43, and 44 are connected. A controlling IC 45 is separately provided at a bottom of the circuit board 41 and electrically connected to the three LED chips 42, 43 and 44 for controlling the on/off of the three LED chips to produce changeful color light. The LED package of FIG. 4 allows a reduced volume of the LED. However, the light-emitting element must include a printed circuit board as a carrier for the LED chips 42, 43, 44 and the controlling IC 45. In addition, since the LED chips 42, 43, 44 and the controlling IC 45 are located at the top and the bottom, respectively, of the circuit board 41, the light-emitting element could not be mass-produced on an automated machine and therefore requires more time to manufacture.